Hemostasis is the human body's response to blood vessel injury and bleeding. Hemostasis involves a coordinated effort between platelets and numerous blood clotting proteins (or clotting factors), resulting in the formation of a blood clot and the subsequent stoppage of bleeding.
Various methods have been introduced to assess the potential of blood to form an adequate clot and to determine the blood clot's stability. Common laboratory tests such as thrombocyte counts or the determination of fibrin concentration provide information on whether the tested component is available in sufficient amount, but some of those tests might not answer the question of whether the tested component works properly under physiological conditions. Other laboratory tests work on blood plasma, which may impose additional preparation steps and additional time beyond what is preferred, for example, in the point-of-care context (e.g., in a surgical theater during a surgical operation).
Another group of tests to assess the potential of blood to form an adequate clot is known as “viscoelastic methods.” In at least some viscoelastic methods, the blood clot firmness (or other parameters dependent thereon) is determined over a period of time, for example, from the formation of the first fibrin fibers until the dissolution of the blood clot by fibrinolysis. Blood clot firmness is a functional parameter which contributes to hemostasis in vivo, as a clot must resist blood pressure and shear stress at the site of vascular injury or incision. In many cases, clot firmness may result from multiple interlinked processes including coagulation activation, thrombin formation, fibrin formation and polymerization, platelet activation, and fibrin-platelet interaction.
To isolate and test particular functions of thrombocytes, fibrinogen, and other factors in a blood sample, reagent compounds can be mixed with the blood sample to activate or inhibit certain components in the blood sample. In some commercially available point-of-care blood testing systems, reagents are injected into a disposable plastic cup containing a blood sample, and the cup is then engaged by the control console of the blood testing system to evaluate characteristics of the coagulation/clotting of the blood sample.
Assorted assays require specific reagents that must be added according to a strict timed schedule or based on a particular order. A manual operator can achieve this by using pipettes for the dispensing and measuring of the reagents, blood, and mixed samples. However, this task is manually intensive. Many automated systems for testing blood have been implemented but they experience problems of blood leakage that prematurely adds reagents to the blood or fails to provide the appropriate reagents to the blood in the correct order.